The phagocytosis associated metabolic, enzymatic and antimicrobial processes of leukocytes collected from animals x-irradiated, whole body and at selected hematopoietic organs, are being investigated. Studies specifically related to the peroxidase-hydrogen peroxide chloride antimicrobial system are currently being emphasized. A peroxidase isolated from spleen lymphocytes is of particular interest. The effect of x-irradiation on host-defense mechanisms, both cellular and humoral, and their possible relationship to the lymphocyte peroxidase-H2O2-Cl negative ion system will be studied. BIBLIOGRAPHIC REFERENCES: Sbarra, A.J., Selvaraj, R.J., Paul, B.B. and Mitchell, G.W., Jr. Biochemical, functional and structural aspects of phagocytosis. International Review of Experimental Pathology, 1975, in press; Sbarra, A.J., Selvaraj, R.J., Paul, B.B., Poskitt, P.K.F., Strauss, R.R., Mitchell, G.W., Jr. and Louis, F. The peroxidase-H2O2-chloride antimicrobial system of leukocytes. Proc. 1st Intersectional Cong. of the Inst. Assoc. Microb. Soc., Tokyo Univ. Press, 1975, in press.